Expand semantics of Array from MutableSequence to MutableMapping

[nmigen-issue-migration]

Issue by whitequark
Sunday May 12, 2019 at 13:25 GMT
Originally opened as m-labs/nmigen#66

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An Array is essentially a mux, and there are several equally valid ways to drive a mux. Currently only straight binary is supported. It would be nice to also have one-hot and priority encodings, since all of these are trivially representable directly in RTLIL and Verilog.

One thing to note is that one-hot and priority are one and the same unless parallel_case is used.

[nmigen-issue-migration]

Comment by whitequark
Wednesday Sep 18, 2019 at 02:21 GMT

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The most idiomatic way to do this is to make the Array associative, and make sure that initializing it with a list uses consecutive indices. (The indices still all have to be integers; possibly enums?)

[nmigen-issue-migration]

Comment by whitequark
Saturday Oct 12, 2019 at 23:29 GMT

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This is a self-contained feature that doesn't have backwards compatibility concerns, so it doesn't have to be in 0.1.

[whitequark]

I've never seen anyone express any interest in this feature, and it's not trivial to implement because of the highly special treatment of ArrayProxy today. Because of that I'm closing the issue.

To implement this, Array should be rewritten so that ArrayProxy is a plain UserValue (perhaps we should call those CustomValue or something instead), and then it will be quite easy to expand its semantics, since it will no longer involve nMigen internals.

[whitequark]

This has been requested on the Aug 3rd meeting: https://freenode.irclog.whitequark.org/nmigen/2020-08-03#1596478574-1596478045; reopening since the reason for closing was that "seemingly no one wants this".

[whitequark]

This was reopened for the benefit of lkcl, who is no longer participating in the project. I think we can safely close this back as "no one (worth caring about) wants this".